Elongated electrode leads, in particular stimulation electrode leads, are an important component of many electric systems that are used in medicine for diagnostic and/or therapeutic purposes, such as (for example) pacemakers, defibrillators, neurostimulators, and catheter systems.
FIG. 1 shows the basic structure of an implantable defibrillation arrangement 1, as is known from U.S. Pat. No. 5,531,766. In order to stimulate the heart H of a patient P, a defibrillator 3 is electrically connected to an electrode lead 5′, which here bears a special electrode (“shock electrode”) 7, which is located at the distal end thereof and is implanted in the patient's heart. Defibrillation is performed via a current path between this electrode and a counter electrode that is located at a distance from the heart. The housing 8 of the defibrillator 3, which contains the units for detecting heart signals and generating electric impulses, can act as a counter electrode. Alternatively, a counter electrode can be attached to the electrode lead or on the outside of the housing.
Stimulation electrode leads usually have a supply lead structure with a distal end including conductive contacts or electrodes, which produce an electrical connection to the surrounding tissue and/or organ of a patient and which are provided for measurement and/or stimulation purposes. If a stimulation electrode lead has several of such electrodes, the supply lead structure may also include several conductors insulated from one another, which are often arranged in a coaxial manner.
FIGS. 2a-2c show a schematic representation of a standard stimulation electrode lead 5, in which two electrodes 2, 4 are present on the distal end of the supply lead structure 10, wherein one electrode (tip electrode) 2 forms a contact at the end of the lead structure 10 and the other electrode (annular electrode) 4 forms an annular contact around the lead structure 10. Since two electrodes are present, the supply lead structure 10 includes two leads 6, 9, which are arranged coaxially.
The stimulation electrode leads can be passively fixable electrode leads (FIG. 2a), wherein the inner supply lead 6 is fixed relative to the outer supply lead 9, or actively fixable electrode leads (FIG. 2b-c), wherein the inner supply lead 6 is moveable relative to the outer supply lead 9. In the latter case, the inner supply lead 6 may be rotationally displaced relative to the outer supply lead 9 in order to introduce or screw the tip electrode 2 into the tissue. In particular, a tip electrode 2 may have the shape of a screw helix.
In both configurations, the outer supply lead 9 of the supply lead structure 10 leads to the annular electrode 4 and the inner supply lead 6 leads to the tip electrode 2. The contact between the supply leads and the electrodes is carried out either directly (FIG. 2a) or by a conductive connection element (FIG. 2b-c), e.g., a mounting fitting 11 or an electric cable 12.
Although this construction is relatively simple from a mechanical viewpoint and is easy to implement structurally, it can have negative effects from an electrical viewpoint. Stimulation electrode leads of this type can lead to certain problems when they are exposed to electromagnetic fields generated by modern examination and diagnostic equipment.